January 2016
doc.: IEEE 802.11-16/0091r2
Regarding HE NDPA frame for DL Sounding
Sequence
Date: 2016-01-18
Authors:
Name
Affiliations
Narendar Madhavan
Toshiba
Address
Phone
email
[email protected]
.jp
Masahiro Sekiya
Toshihisa Nabetani
Tsuguhide Aoki
Tomoko Adachi
Kentaro Taniguchi
Daisuke Taki
Koji Horisaki
David Halls
Filippo Tosato
Zubeir Bocus
Fengming Cao
Submission
Slide 1
Narendar Madhavan, Toshiba
January 2016
doc.: IEEE 802.11-16/0091r2
VHT Compressed Beamforming frame format
• In 11ac , STAs (or beamformees) decide how much to feedback
• 8.4.1.47 [1] VHT MIMO control field is included in the VHT compressed
beamforming frame format
• The channel width, number of sub-carrier grouping, codebook etc., are
decided by the STAs depending on their capability
• Depending on the values chosen for these parameters, the size of the feedback
matrix varies
Submission
Slide 2
Narendar Madhavan, Toshiba
January 2016
doc.: IEEE 802.11-16/0091r2
VHT Compressed Beamforming frame format
• There are three main factors that determine its size:
1.
Bandwidth: wider channels have more subcarriers, so the feedback matrix must be larger to
accommodate them.
2.
Higher the number of sub-carriers, larger the matrix.
3.
802.11ac allows two different bit representations of the angle values to enable devices to use
higher resolution when necessary.
• Multi-user MIMO requires higher resolution to avoid inter-user interference
• In 11ac, All these parameters are decided by the beamformee or STA.
In 11ax, if the same rule is followed
there is an imminent problem:
Multiple STAs send compressed
beamforming frames of varying duration sizes
in UL MU mode
Submission
Slide 3
Narendar Madhavan, Toshiba
January 2016
doc.: IEEE 802.11-16/0091r2
HE DL Sounding
• We have the following in the current SFD [2]:
•
To solicit the STAs to send Compressed Beamforming frames in the UL MU
mode simultaneously, Trigger frame includes the PPDU length and MCS
•
AP decides the UL PPDU length and MCS to be notified to the STAs
•
STAs may not be able to adjust to the PPDU length mentioned in the Trigger
frame
•
•
Feedback matrices are prepared with different parameters determined at multiple
beamformees immediately after the reception of NDP frame
STAs may not be able to adjust to the MCS in the Trigger frame
Submission
Slide 4
Narendar Madhavan, Toshiba
January 2016
doc.: IEEE 802.11-16/0091r2
Setting compressed beamforming frames’
UL MU PPDU length
• AP has to notify the PPDU length in the Trigger frame to solicit
Compressed beamforming feedback frames in UL MU
• Option 1: AP sets the longest possible PPDU length of compressed
beamforming frames to all the STAs in the trigger frame
• Option 2: STA adjusts to the PPDU length provided in the trigger
frame irrespective of the feedback frame size generated locally
• Option 3: AP notifies the feedback parameters to the STAs in the
Trigger frame
• Option 4: AP notifies the feedback parameters to the STA in the HE
NDPA frame
Submission
Slide 5
Narendar Madhavan, Toshiba
January 2016
doc.: IEEE 802.11-16/0091r2
Notifying UL MU PPDU length for Sounding
Option 1:
Choose the largest PPDU duration possible and notify using the Trigger frame
Pros:
•
Lowest MCS, with high resolution for the feedback matrix, all STAs will be able to align to the
PPDU length
Cons:
•
Inefficient as most of the STAs will have to pad
Option 2:
STAs decide the feedback parameters and adjusts to the PPDU length indicated in the Trigger
frame
Pros:
•
Feedback matrix can be constructed immediately after NDP frame
Cons:
•
After receiving the trigger frame, STAs have to reconstruct the frame using the given PPDU length
•
Might be difficult to perform this within TBD IFS after Trigger
•
If the STAs are not able to prepare the feedback matrix frame or match the PPDU length they have
to be polled again.
Submission
Slide 6
Narendar Madhavan, Toshiba
January 2016
doc.: IEEE 802.11-16/0091r2
Notifying UL MU PPDU length for Sounding
Option 3: AP notifies necessary parameters for sounding to the STAs in the
Trigger frame
Pros:
•
Can be included in the Per-STA info fields or the common info field
Cons:
• STAs may not be able to construct the desired feedback frame within TBD IFS after
receiving Trigger
• STAs start making the feedback matrix after receiving NDP frame and have to adjust to the
parameters indicated in the Trigger frame later
Option 4: AP notifies necessary parameters for sounding to the STAs in the HE
NDPA frame.
Pros:
• Can define it in the Per-STA info fields or a common info field
• Ample time to prepare the feedback matrix after receiving NDP frame
Cons:
• A new HE NDPA frame needs to be designed
Submission
Slide 7
Narendar Madhavan, Toshiba
January 2016
doc.: IEEE 802.11-16/0091r2
Summary
• The necessity of an HE AP to notify certain parameters
to solicit STAs (or beamformees) to generate
beamforming feedback matrices was discussed
• Parameters include sub-carrier grouping , Codebook,
channel width etc.
• These parameters notified before the reception of HE
NDP frame is preferred
• Option 4: AP notifies the necessary parameters for sounding to the STAs
in the HE NDPA frame.
• Enables STAs to start preparing the compressed beamforming frames
immediately after the reception of HE NDP
• Need to design a new NDPA frame for HE DL Sounding
Submission
Slide 8
Narendar Madhavan, Toshiba
January 2016
doc.: IEEE 802.11-16/0091r2
References
• [1] IEEE Std 802.11ac-2013
• [2] 802.11-15/0132r9 “Specification Framework for
TGax”
Submission
Slide 9
Narendar Madhavan, Toshiba
January 2016
doc.: IEEE 802.11-16/0091r2
Straw Poll 1
Do you agree to add to the TG Specification Frame work
document?
• x.y.z. An HE AP indicates the necessary TBD parameters
so that multiple HE STAs can construct the compressed
beamforming feedback frames immediately after receiving
the HE NDP frame
Submission
Slide 10
Narendar Madhavan, Toshiba